In general, most, if not all, DBMS systems are required to recover without loss of data or transactions after some types of system failures without the need to reference system backup data sets. This recovery capability is a normal part of the operation and restarting of the DBMS. Obviously for those failures of a more catastrophic nature, use of backup data is required.
U.S. Pat. No. 4,507,751, Gawlick et al., entitled Method and Apparatus for Logging Journal Data Using a Write Ahead Dataset, issued Mar. 25, 1985, exemplifies a transaction management system wherein all transactions are recorded on a log on a write-ahead dataset basis. As described in this patent, the protocol requires a change to the database is first recorded on the log and only then written to its external storage. The computing apparatus includes volatile storage for storing a log buffer and a non-volatile storage for storing a journal log. Non-volatile storage means are provided for storing in a write-ahead dataset a plurality of short data blocks. The log buffer contents are written to the write-ahead data set responsive to a process epoch occurring before the log buffer is filled. The log buffer contents are written to the journal log upon the log buffer being filled. The redoing or undoing of database changes is made with reference to the write ahead dataset only in the case of a system failure resulting in loss of log buffer data not yet written to the journal log; otherwise database changes are redone or undone with reference to the log buffer or journal log. The method described by Gawlick, et al. includes the requirement that upon the being restarted, the DBMS must have a way to restore the integrity of the data based on the logs.
When a data processing system is in the process of backing up data in either a streamed or batch mode system, each process, task or application within the data processing system is affected, since the processes supporting streamed or batch mode operations are suspended for the duration of the copying. Those skilled in the art will recognize that this event is typically referred to as a “backup window.” In contrast to batch mode operations, log based or transaction management applications are processed in the interactive mode. Such transaction management applications eliminate the “backup window” by concurrently updating an on-line dataset and logging the change. However, this type of backup copying results in a consistency described as “fuzzy.” That is, the backup copy is not a precise “snapshot” of the state of a dataset/data base at a single point in time. Rather, a log comprises an event file requiring further processing against the database.
As is well known in art, the steps in a computer implementable method can be used to create a computer program product stored on a portable computer usable media. The media with the computer program product stored thereon is an article of manufacture capable of causing a computer system to execute the computer program product and thereby to perform the method. The computer program product may also be transmitted electronically to a computer which stores the program on its media for recall and execution as required.